1: The Usual Suspects - Kujan realises that he has been conned...

(Bryan Singer, US, 1995)

"It was one of those rare occasions when you could lie to an audience and because there were so many aspects to the film the audience would accept lies - it made the ending all the more exciting and powerful."

That is how director Bryan Singer remembers the scene that tops the Observer poll. "The film won two Academy Awards but in a way this is more significant because then we were up against the best films of 1995, while this survey is comparing a moment in The Usual Suspects to all the great moments in film history." The nature of the list also appeals to Singer: "Films to me are great lines and great moments - it is amazing to me that we should come out top. It is a testament to how much people like to be tricked: if you trick them the right way, they will love you forever; if you get it wrong, you will never work again."

The whole film is built on lies. Five criminals meet at a police line-up, plan and execute a successful robbery. And they are then approached by the arch criminal Keyser Soze via his henchman, the lawyer Kobayashi, played by Pete Postlethwaite. He makes them an offer - work for the devil or die. The tale is told in flashback by Kevin Spacey's character, the crippled Verbal Kint - already granted immunity from prosecution - as he is interrogated by customs officer Dave Kujan, played by Chazz Palminteri.

But this revelation scene is not the original. Singer screened the first version for two friends - his agent and his lawyer - before realising that it was, "too flat?it was confusing and just kind of died". It had the crashing coffee cup falling out of Kujan's hand, the bulletin board and the fax with the face of Keyser Soze, which seems to take forever to come off the machine. But after that first screening, Singer introduced the visual flashbacks as Kujan scans the board and finally realises that he has been conned by Spacey's Kint - aka Keyser Soze - who is shuffling out of police headquarters after being released by Kujan.

Singer added audio flashbacks. So in hindsight we hear from disembodied voices, with Spacey's saying: "It's all there, I'm telling it straight, I swear," as Kujan scans the board and finds references to some of the places and characters from Spacey's elaborate lie staring down from the board.

"It works because of the way Kevin carries the moment, the choice of music - how it shifts gear and takes a completely different rhythm from the rest of the film," says Singer. "There are all kinds of scenes and pieces of the film being played out before your eyes - the images are flooding down from the bulletin board. The coffee cup goes crashing in slow motion and all the time you are seeing images from the film that you thought meant one thing but you now realise mean something completely different. We pulled together every bit of sound which hinted that Kevin was Keyser Soze. The flashbacks and audio were all keenly placed to sit with certain images and then we stuck all the magnetic tape together and waited to see the result."

The scene was the idea of screenwriter Christopher McQuarrie. He and Singer had made a low-budget film, Public Access, in 1993 that won an award at the Sundance film festival. The duo was seeking a new project and McQuarrie came up with the idea of five criminals meeting at a police line-up. The bulletin board scene was the second he wrote and the film was then effectively written in reverse.

"It is one of the few times I can watch something that I have done. Obviously I am biased, but I think it was a successful surprise, and it had been a long time since a surprise ending had actually caught people by surprise."

2: Psycho - The shower scene

"Mary started to scream, and then the curtains parted further and a hand appeared, holding a butcher's knife. It was the knife that, a moment later, cut off her scream. And her head." Bang. End of chapter three.The most famous screen murder of all time is over in a flash in Robert Bloch's original novel: three lines, in fact.

In Joseph Stefano's screenplay, 'Mary' became Marion, her head stayed mercifully on, and this goreless, staccato passage was transformed by Hitchcock, 'pictorial consultant' Saul Bass, editor George Tomasini and composer Bernard Herrmann into a landmark of postwar cinema and one of the most imitated and parodied sequences ever committed to film. What's more, on a non-academic level, it's as intensely powerful today as it ever was.

Famously shot on an $800,000 shoestring in six weeks with a crew from Hitchcock's TV series, Psycho was dismissed by the critics on its release - partly because there were no preview screenings - but it made $15 million in its first year, earned four Oscar nominations and accidentally kickstarted the slasher movie genre (not to mention three mediocre sequels of its own). It has since been listed by the National Film Registry at the Library of Congress, slowed down and turned into an art installation, sent up in The Simpsons and remade, shot for shot, by Gus Van Sant (proving, if nothing else, that colour ruins it).

The 45-second shower scene, shot in seven days using 70 separate camera set-ups, is not just the most memorable in the film, it is the plot pivot, the unexpected - and unexpectedly vicious - dispatch of the leading lady (Janet Leigh) halfway through. Indeed, Marion Crane's spontaneous theft of $40,000 from her realtor boss and subsequent paranoid flight from Phoenix is a lengthy MacGuffin - it is her murder by motelier Norman Bates (Anthony Perkins) dressed as his dead mother that signals the 'beginning' of the story. As such, the shower is unique in that it can legitimately be viewed and appreciated in isolation as a bravura example of the filmmaker's art, or enjoyed as the narrative masterstroke in a very clever movie. (It's easy to see why Hitchcock banned exhibitors from letting in audiences once Psycho had started.)

The trivia of Hitchcock's most celebrated and raked-over scene sometimes threatens to overtake its visual power, but nuggets like these are hard to resist: for instance, Marion could have been played by Eva Marie Saint, Shirley Jones, Lana Turner or Hope Lange. The silhouetted 'Mother' behind the shower curtain was played by Ann Dore (one of five different uncredited actresses responsible for creating Mrs Bates - three for her physical scenes, plus two for her voice, spliced with that of Paul Jasmin, an actor pal of Tony Perkins). The censors demanded the removal of one shot in which they believed Leigh's nipple was visible, but in actual fact, only her head, feet and arms are seen - the rest is stand-in Marli Renfro, a nude model, whose dignity was preserved through judicial use of moleskin patches and glue.

The blood that swirls downs the plughole is chocolate sauce, the stabbing sound effects were created by violating a Turkish melon, Janet Leigh postponed the filming twice due to a cold and then her period, and for the final shot of her inert form, she wore contact lenses to create the dilated pupils.Perhaps the scene's biggest talking point down the years has been the contention that graphic supremo Saul Bass, having storyboarded the scene, also directed it. He made this claim himself in 1973, presumably sore that Hitchcock had written his contributions to this and the Arbogast murder scene out of the story. (Bass had not only storyboarded both, he actually shot and assembled a montage to prove that the shower scene would work). However, Janet Leigh has since put the records straight: "Saul Bass was there for the shooting, but he never directed me."Whatever. When Francois Truffaut interviewed Hitchcock in 1962, the director said that his 'main satisfaction' regarding Psycho was that it 'had an effect on the audience' - a desire more than realised by the shower scene's continuing legacy. "It wasn't a message that stirred the audience,' commented Hitchcock. 'Nor was it a great performance?They were aroused by pure film."

3: The Third Man - Harry Lime appears

It nearly wasn't him. Noel Coward could have made the most famous entrance in cinema history. Then producer David O. Selznick wanted Robert Mitchum to play legendary racketeer Harry Lime. That particular star put paid to his chances after being arrested and imprisoned for marijuana possession in 1948. So Welles it would be then. Selznick initially resisted the Hollywood maverick: Welles's box-office appeal had slumped disastrously.

In reality Welles's appearance was so late in the film his star billing could seem undeserved. He didn't appear in The Third Man until an hour into the film. And even then he didn't speak. Naive American writer, Holly Martins (Joseph Cotten), was in ravaged post-war Vienna trying to unravel the mystery of his best friend Lime's apparent death. Up to this point moviegoers had been entranced by Reed's noir-ish vision of a city near breakdown. Incidentally, Observer readers found more moments to savour in The Third Man than any other film. Harry Lime's cuckoo clock speech narrowly failed to make it on to the final list. But there was no doubt about the film's most treasured scene. As is often the case, an odd twist of fortune played a part in the circumstances leading to the film's pivotal scene.

Characteristically, Welles was less than committed when working for another director. He'd often disappear, trying to raise funds for his Othello adaptation from financiers across Europe. On one occasion he was in Rome while needed on set. In desperation Reed often ordered assistant director Guy Hamilton to take his place so he could shoot an ominous figure running thorough the streets. "He made me dress up in a big black coat with padded shoulders because I was rather skinny," he recalled.

Fortunately Welles was around for his most famous close-up. The night scene had been smartly set up. Moments after Lime's former girlfriend, Anna Schmidt, told Martins her cat 'only likes Harry', it had stolen outside and snuggled against the shoes of a mysterious man hiding in a doorway. When a drunk Martins leaves her flat, he is aware of a man on the other side of the street. Martins taunts him: "Cat got your tongue? Come on out! Come out, come out, whoever you are." He rouses an indignant Frau who switches on a light above the door illuminating Lime's face.

At the realisation that his plans to disappear have been undone by chance, Lime smiles enigmatically. His face is mischievous, not malicious. The film's villain clearly likes a joke. For all the Third Man's virtues - a British Film Institute poll saw it voted the best British film ever - the scenes with Welles dominate. Whether he is hiding in a doorway or philosophising on a Ferris wheel, Welles is the film's iconic motif.

At a time when independent sensibilities seem to be encouraged in Hollywood, Welles is the patron saint of pigheadedness. It's hardly surprising contemporary left-fielder Tim Robbins' latest film The Cradle Will Rock is based on one of Welles's early artistic struggles in the theatre. Welles displayed little humility on the set of The Third Man; he frequently offered directing tips to Reed and rewrote his own lines, improvising the cuckoo clock speech. "It's true that Orson suddenly produced it while on set," says Hamilton. "Carol said: 'It's a goody, let's use it.'" On screen, as in life, he cut a larger-than-life figure. A decade later he emerged as a grotesque villain in his own creation Touch of Evil, but in The Third Man he played the most appealing of characters: a charismatic baddie.

More Third Man moments and the strange case of Citizen KaneNaturally, many films received votes for more than one moment. Casablanca and Jaws both did themselves no favours in terms of the final list by throwing up so many memorable scenes. Citizen Kane (below) suffered more than any other film from this effect, votes for which were so varied that no one moment made the final 100. (By contrast, the greatest beneficiary was our poll topper, The Usual Suspects which, beyond the winning moment, barely received a mention.) Of our 100, The Third Man elicited the greatest variety. Here's a few of the nearly list.

•Harry Lime defends himself to Martins on a Ferris wheel ride. "In Italy for 30 years under the Borgias they had warfare, terror, murder, and bloodshed, but they produced Michelangelo, Leonardo da Vinci and the Renaissance. In Switzerland they had brotherly love - they had 500 years of democracy and peace, and what did that produce? The cuckoo clock."

•Orson Welles's hands appear through the grating at street level, grasping the air, after being shot trying to escape the police in the sewers.

•A moon-faced boy, holding a ball, shouts at Holly Martins and Anna Schmidt as he chases them away from the murder scene of the vital witness, provoking suspicion from on-lookers that Martins was responsible.

4: 2001: A Space Odyssey - From flying bone to space ship

Kubrick's beautiful but baffling sci-fi opus billed itself as The Ultimate Trip, spanning many, many thousands of years, from the dawn of man to the first, futuristic steps into space and, with typically Kubrick hubris, 2001 announces this with one simple, majestic cut.

Having introduced us to a jabbering community of ape-men, Kubrick reveals a mysterious, coal-black and clearly alien totem that seems to exert a strange influence over this primitive race. Ape-gangs clash, tempers fray, and when their leader thwacks down his club into a pile of bones, he sends them flying into the air - which Kubrick seamlessly matches with a jump-cut that shows a spaceship seeming to follow its graceful trajectory into the starry void of space, accompanied by the triumphant strains of Also Sprach Zarathustra.

This wordless leap is typical of Kubrick's open-ended, psychedelic movie: although it lasts some two hours and 20 minutes, there are only 40 minutes of dialogue, and the significance is left to the viewer's imagination.

The film's co-creator, Arthur C Clarke, claimed that the film was meant to be unsolvable, going so far as to claim that "if you understand 2001 completely, we failed. We wanted to ask more questions than we posed". Kubrick was never happy with this explanation and claimed that Clarke was speaking 'facetiously'. However, he did believe in preserving the film's mystery, asking Playboy magazine, "How much would we appreciate La Gioconda today if Leonardo had written at the bottom of the canvas: 'This lady is smiling slightly because she has rotten teeth' or 'because she's hiding a secret from her lover'? It would shut off the viewer's appreciation and shackle him to a 'reality' other than his own. I don't want that to happen to 2001."

View from the stalls"The moment is special because it manages to encompass the entire evolution of the human race in one graceful visual metaphor. The ape has used a weapon for the first time and this sets the course of development that culminates in the nuclear bomb". Robert West, Oxford

5: Apocalypse Now - Dawn helicopter attack

(Francis Ford Coppola, US, 1979)

Apocalypse Now was method filmmaking: the film that was as insane as the war itself. And never more so than during the making of the film's showpiece: the scene where insanely gung-ho Colonel Kilgore (Robert Duvall) and his Air Calvary helicopters swarm out of the dawn light to flatten a Vietcong village, speakers blasting out Wagner's 'Ride Of The Valkyries' as they go (the great film critic Pauline Kael bizarrely tried to dissuade Coppola from using the music on the grounds that it had already been used in a European arthouse movie).

Having already set up the hugely expensive scene, Coppola tried to bully the US secretary of defence into providing a lifting helicopter for the scene. The helicopters they did have were borrowed from Filipino dictator Ferdinand Marcos, and were called away in the middle of the shooting of the scene to be used in a real war against Communist guerrillas. "We just heard they're taking away five of our helicopters," Coppola rages in the documentary Hearts Of Darkness, clearly no longer able to realise he was only making a film about a war. When he did have the choppers, all he could do was complain about the incompetence of the Filipino pilots.

But the result is stunning, the craziness and the appeal of war brought together. "Men play strange games to break up the boredom of being in the war," Duvall once said, explaining Kilgore, the man who insists on having his troops surf in the middle of battle. But the real genius of the scene comes not from the grandiose explosions, or even the strange beauty of the attack helicopters, but from some subtle acting: the incredulous expression on Martin Sheen's face as he watches Kilgore in action.

6: Blade Runner - Batty's dying speech in the rain

"I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near the Tanhauser Gate. All these moments will be lost in time. Like tears in rain. Time to die."

After Rutger Hauer (Batty) delivered his final soliloquy, the surrounding crew applauded and a few even cried. It wasn't just the replicant's final poignant words that stirred them. Finishing the rain-sodden scene marked the end of an arduous shoot. The exhaustion on Harrison Ford's face as he watches his man-made adversary's demise isn't just acting. He was knackered. Originally Hauer's speech was much longer but the actor persuaded Scott to cut the dialogue saving the audience another protracted death scene. "His batteries are going. He has no time to say good-bye, except maybe to briefly talk about things he'd seen. 'Life is short' - boom!"

With Scott's permission he cut out the beginning and improvised the last lines. Although Hauer crafted the speech to suit himself, he paid tribute to screenwriter David Peoples for doing 'a really beautiful job'. "I loved those images he came up with - 'c-beams glittering near the Tanhauser gate, attack ships off the shoulder of Orion'. I thought they were really interesting, even if you didn't understand them."

7: The Great Escape - The Cooler King escapes on his motorbike

Hot off the back of The Magnificent Seven but basically still a TV actor, Steve McQueen almost turned down The Great Escape ("I just did two WWII flicks and they both died in the stretch", he told director Sturges, referring to Hell Is For Heroes and The War Lover). In the end, he took it on the proviso that he was allowed to ride a motorcycle - a typically brattish, macho McQueen demand, but one which sealed his iconic fate, for the climactic two-wheeled leap over a six-foot barbed-wire fence remains the defining image of the film.McQueen, playing loner POW Hilts ('the Cooler King') breaks out of the prisoncompound, steals a motorbike from a German soldier using piano wire across a road, and dons his uniform. It is actually McQueen in the saddle during the resulting chase - in fact, he also doubled for a German soldier in pursuit ("With exceptional cutting," commented Sturges, "Steve could've played the entire German motorcycle corps"). The famous jump over the wire was achieved by McQueen's stunt double, long-time pal and bike shop owner Buddy Ekins, on a souped-up Triumph. With the cameras rolling, he cleared it in one take ("Nothing like that had ever been done before," said Ekins).

Ironically, the heroic jump does not lead to Hilts' escape - he falls at the next fence - but the scene made McQueen. In Britain, mods and rockers went to see the film over and over again for the jump; they stood up and cheered every time.

8: Casablanca - Rick and Ilsa part at the airport

By all accounts, it drove Ingrid Bergman (Ilsa) crazy. As scriptwriter Howard Koch recalled, "The ending of the film was in the air until the very end. We thought of many possibilities and finally decided on the one that was in the film." Of course, any other ending would have ruined the film, both as a tragic love story and as a great piece of anti-fascist propaganda. As it was, these were the words Warner Bros's squad of writers cobbled together for Rick (Humphrey Bogart) and Ilsa to say as they stood on the runway:

Rick: Inside of us, we both know you belong with Victor. You're part of his work, the thing that keeps him going. If that plane leaves the ground and you're not with him, you'll regret it. Maybe not today. Maybe not tomorrow, but soon and for the rest of your life.Ilsa: But what about us?Rick: We'll always have Paris. We didn't have, we lost it until you came to Casablanca. We got it back last night.Ilsa: When I said I would never leave you.Rick: And you never will. But I've got a job to do, too. Where I'm going, you can't follow. What I've got to do, you can't be any part of. Ilsa, I'm no good at being noble, but it doesn't take much to see that the problems of three little people don't amount to a hill of beans in this crazy world. Someday you'll understand that. Now, now... [He wipes away her tear] Here's looking at you kid.

9: Planet of the Apes - Taylor finds the Statue of Liberty

(Franklin J Schaffner, US, 1967)

For all the recent talk about stunning twists in movies from Sixth Sense to Fight Club, none has the impact of the end of Planet Of The Apes. This is one surprise ending that strengthens, rather than undermines, the meaning of what's gone before. It still sends a shiver up the spine - and it rejuvenated the career of Charlton Heston (Taylor), leading to the similarly minded Soylent Green and The Omega Man and making him the most improbable icon for nuke-hating hippies.All the way through the film, stranded astronaut Taylor believes he is on an Earth-like planet. But having escaped into the Forbidden Zone, he comes across a strange object on the beach and as we begin to see it is the Statue Of Liberty, it slowly dawns on Taylor where he is and what has happened:

"You did it, didn't you...You maniacs! You blew it up! Damn you! God damn you all to hell!"

In the original script, Taylor just says 'My God!' Heston claims that he wrote the speech used in the film. But as Heston's diaries record, in 1967 'goddamn' was still banned by the Hollywood Production Code. Fortunately, Heston successfully argued that he was using the expression precisely: "It's surely acceptable in the context of this speech; Taylor is literally calling on God to damn the destroyers of civilisation." It was one of the last stands that old Hollywood morality would make.

View from the stalls"Charlton Heston finds the Statue of Liberty buried in the sand and screams at the sky, 'God damn this world to hell.' I often shout that at Waterloo station when my train has been cancelled again." Karen Gilchrist, Middlesex.

10: Some Like It Hot - 'Well, nobody's perfect'

"It's always very difficult for me to say 'this is mine and this is his' said Wilder recently. "Always except, of course, I have to give [longtime co-screenwriter] Diamond credit for 'Nobody's Perfect.'The late I.A.L. Diamond deserves ample praise for penning one of the movies' greatest payoff lines: Joe E. Brown's sanguine response to cross-dressing Jack Lemmon's revelation that 'she' is actually a he: 'You don't understand, Osgood! Aaah? I'm a man!'

Lemmon and Tony Curtis shared plenty of sparkling, Wildean wit in Some Like It Hot, playing a couple of musicans who, having witnessed the St Valentine's Day Massacre, flee for their lives disguised as the newest members of an all-girl band.

Ironically, the film's best line went to Brown, by then a forgotten silent movie journeyman. It also nearly didn't make it. Diamond originally suggested the line as a temporary solution when the pair failed come up with a final flourish. After a test audience 'exploded' at a preview screening, they kept it. "I was asked by many people, 'What is going to happen now?' And I always said, 'I have no idea. Leave it up there on the screen. You cannot top that.'"